In Situ Measurement of Water at the Organic Coating/Substrate Interface.
In Situ Measurement of Water at the Organic
Nguyen, T.; Byrd, W. E.; Bentz, D. P.; Lin, C.
Progress in Organic Coatings, Vol. 27, 181-193, 1996.
organic coating; substrate interface; water measurement
In situ and quantitative information on the water layer
at the organic coating/substrate interface is crucial
for understanding and preventing the failure of organic
coating systems. A technique, based on a two-layer
model derived rigorously from internal reflection
theory, has been developed for measuring in situ the
thickness and amount of the water layer at the organic
coating/substrate interface. The technique gives new
insight into the processes by which water degrades the
coating/substrate bonds. In this technique, a
transparent or an opaque organic coating of sufficient
thickness is applied to an internal reflection element
(IRE) with or without a thin metallic film, which is
used as the substrate. A water chamber is attached to
the organic-coated specimen. After adding water to the
chanber, Fourier transform infrared-multiple internal
reflection (FTIR-MIR) spectra are taken automatically at
specified time intervals without disturbing the
specimens or the instrument. Water uptake in the
coating and FTIR-MIR spectra of water on the
coating-free substrate are also used for the analysis.
Examples of clear and pigmented coatings on untreated
and treated substrate surfaces are given to demonstrate
the technique. Results of water accumulation at the
coating/iron interface with and without applied
electrical potentials are given. In addition to
measuring water at the coating/substrate interface, the
technique provides a means for studying the transport of
water through a coating adhered to a substrate.
Information on water at the interface and its transport
properties through coatings applied to a substrate is
valuable for interpreting corrosion, blistering and
delamination of organic coating systems, and for
developing models for use in predicting the service
lives of protective coatings.